Composite sheathing materials are widely used in the building and construction industries as wall components or panels, for sheathing the walls which form the exterior surfaces of a building. Such sheathing materials may be exposed to liquid water from rain or melting snow from outside the building, and moisture vapor from inside the building. Preferred sheathing materials would prevent the passage of liquid water from the exterior to the interior of the building, while allowing the passage of moisture vapor through the sheathing material from the interior to the exterior of the building. Conventional composite sheathing materials, while preventing the passage of liquid water therethrough, only provide moisture vapor permeability values of up to about 1.5 perms. By the term "perm" as it is used herein is meant the rate of moisture transfer in units of grams/hour/square foot/inch of Hg.
It would be desirable to prepare a composite sheathing material that would substantially prevent the passage therethrough of liquid water while allowing a high rate of moisture vapor permeation.